if your old computer is bootable, open your browser and get your login and password from that...

https://www.digitalcitizen.life/export-passwords-web-browser-csv/

Firefox has a menu option to display saved logins; on the saved login for DU, there is a button to 'Copy' the password. Click that, then open a text editor (like Wordpad) and paste it into a document, That will display it in plain text. I can't speak for other browsers, but if you poke around, you might be able to find something similar.

I'd suggest doing a hex scan of the copied password entries but a lot of times, this is scrambled anyways.

there should be "lost password?" as well as "lost ID?"

Most sites allow you to supply just one vital to get a reset button. It might ask for your email to send a reset link. That's getting to be pretty normal on sites.

There's a signin button on the upper right of the home screen when you're not logged in.

https://www.democraticunderground.com/?com=login

And yes, there's a link for "forgot password?" as well as "forgot username?"

Might want to use the automatic password and login generator in firefox or similar. They can even be synced to other devices like a smart phone or another computer